Sorry for stepping in late, but maybe I can help. If I read your original post correctly, your network is fine, and the SBT works fine, it's only the Naim 272 that has problems. In my mind that means it's the Naim that needs fixing, not the modem, router, etc... Two other things: I like using Roon to control my music playback, it's light years ahead of every other music app I've tried (including iTunes and Naim's own); my family likes streaming via Airplay. The 272 doesn't support either, so even if you get the streaming gremlins sorted, you'll be stuck with Naim's UI. What I did in my system, is shell out a colossal $35 and solve all of the above at one fell swoop.
1. Pick up a Raspberry Pi 3 on Amazon
2. Pick up the recommended cheap micro-USB power supply at the same time
3. Pick up a 8-16 Gb SD card from SanDisk at the same time
4. Follow the directions on the DietPi website (not allowed to provide a link, sorry), but if you google DietPi you'll find it. Once at their website, click "Getting Started" scroll down, and click "Getting Started for step-by-step.
5. Do Step 1
6. Do Step 2, including the optional WiFi part (you can turn it off later, but turn it on to begin with to make everything else easier)
7. Do Step 3
8. Do Step 4
9. Do Step 5 and install the Shairport and RoonBridge packages. Shairport will give you Airplay, Roon Bridge will give you Roon if you wish to try it out (free trial)
The Raspberry Pi can stay on WiFi, or you can hardwire it via ethernet. Works fine both ways and will give you bit-perfect USB input into your 272. If you prefer S/PDIF or BNC even, go to HiFiBerry and get the appropriate digi+ board.
I know, it sounds complicated, but it took me 30 minutes to set up the first time, and I've never used one of these before. Ever since, it's been flawless, high resolution, bit perfect streaming all day every day. Worst case, your out $50 (including Pi, power supply, and SD card). Don't get suckered into expensive power supplies and USB cables, they don't make a difference if your DAC is galvanically isolated and isochronous (I believe the 272 is both).
You'll feel empowered. Let me know if you have questions and I'll help if I can.